Hi sorry am i doing this right?

find all solutions to the equation

$\displaystyle x^6 + 2x^3 + 1 = 0 $

let $\displaystyle u = x^3 $

then $\displaystyle u^2 + 2u + 1 = 0 $

$\displaystyle = (u+1)^2 = 0 $

thus $\displaystyle u^3 = -1 $

$\displaystyle = \sqrt{1} e^{\pi + 2\pi m} $

and then i solve for $\displaystyle m = 0..6 $

is that correct?